The field of the invention is electrical relays having a plurality of magnetically responsive sealed switches of the type which are known for their high reliability, speed of operation and use in adverse operating environments. In this category of switches are the basic dry reed switch and the many variations thereof. A typical relay using reed switches is described in U.S. Pat. No. 3,605,049.
The basic dry reed switch includes a pair of elongated, overlapping reed members which act as both current and flux conductors. The reeds are usually enclosed in a sealed glass envelope filled with an inert gas. When flux flows across the gap between the overlapping reed members, they are pulled together to make electrical contact.
The reed switch is reliable and simple; however, it exhibits the phenomenon known as "contact bounce." When a reed switch is actuated, the contacts close, separate a short distance, and then close again, all within a period from 100 to 400 microseconds after the initial closure. Bounces are recorded on an oscilloscope as a series of high level pulses of short duration. This feature is undesirable because such pulses may falsely trigger solid state digital circuitry. Contact bounce also generates some radio frequency interference, and is responsible for arcing which causes pitting and wear on the switch contacts.
The present invention employs a mercury switch which includes two mercury layers wetting its inner surfaces, one of the layers being movable toward the other in response to an external magnetic field to form a continuous volume of mercury that conducts electricity. Upon removal of the external magnetic field, the movable layer returns to its normal position breaking a filament of mercury drawn from the mercury layer wetting the other surface. As applied to mercury the term "layer" is distinguishable from the terms "pool" and "film." This distinction is explained in U.S. Pat. No. 3,646,490 entitled "Mercury Switch."